The present invention relates generally to the delivery of treating elements by a catheter to a selected site within the vascular system of a patient. More particularly, the present invention relates to method and apparatus for the delivery of a treating element, such as a radiation source, through a catheter to a desired site, such as a coronary artery, for inhibiting wound healing response, such as restenosis following balloon angioplasty.
It is known that the human body""s healing response to wounds typically includes the formation of what is commonly called scar tissue. This response also occurs within the vascular system of a person following injury to a blood vessel. An injury that provokes the formation of scar tissue may occur in various locations within the vascular system, such as in the carotid artery or in coronary bypasses, or in various ways, such as trauma from surgical or diagnostic procedures.
One area of the vascular system of particular concern with respect to such injuries is coronary arteries that are subjected to procedures for removing or reducing blockages due to plaque within the arteries. Partial and even complete blockage of coronary arteries by the formation of an atherosclerotic plaque is a well known and frequent medical problem. Such blockages may be treated using atherectomy devices, which mechanically remove the plaque; hot or cold lasers, which vaporize the plaque; stents, which hold the artery open; and other devices and procedures which have the objective of allowing increased blood flow through the artery. The most common such procedure is the percutaneous transluminal coronary angioplasty (PTCA) proceduresxe2x80x94more commonly referred to as balloon angioplasty. In this procedure, a catheter having an inflatable balloon at its distal end is introduced into the coronary artery, the uninflated balloon is positioned at the stenotic site and the balloon is inflated. Inflation of the balloon disrupts and flattens the plaque against the arterial wall, and stretches the arterial wall, resulting in enlargement of the intraluminal passageway and increased blood flow. After such expansion, the balloon is deflated and the balloon catheter removed.
PTCA is a widely used procedure and has an initial success rate of between 90 and 95 percent. However, long term success of PTCA (as well as the other artery-opening procedures referred to above) is much more limited, due largely to restenosis, or re-closing of the intraluminal passageway through the artery. Restenosis, wherein the vessel passageway narrows to approximately 50% or less of the enlarged size, is experienced in approximately 30 to 50 percent of the patients within six months after PTCA. Restenosis may occur for various reasons, but it is now believed that restenosis is, in significant part, a natural healing response to the vessel injury caused by inflation of the angioplasty balloon.
Vessel injury may occur in several ways during PTCA, including: denudation (stripping) of the endothelium (the layer of flat cells that line the blood vessels); cracking, splitting and/or disruption of the atherosclerotic plaque and intima (innermost lining of the blood vessel); dehiscence (bursting) of the intima and the plaque from the underlying media; stretching and tearing of the media and adventitia (outside covering of the artery) which may result in aneurysmal expansion; and injury to the vessel smooth muscle. Such injury to the vessel typically initiates the body""s own natural repair and healing process. During this healing process, fibrin and platelets rapidly accumulate in the endothelium, and vascular smooth muscle cells proliferate and migrate into the intima. The formation of scar tissue by smooth muscle proliferation, also known as intimal hyperplasia, is believed to be a major contributor to restenosis following balloon angioplasty of the coronary artery.
Prior attempts to inhibit restenosis of coronary arteries have included, among other things, the use of various light therapies, chemotherapeutic agents, stents, atherectomy devices, hot and cold lasers, as well as exposure of the stenotic site to radiation. These therapies have had varying degrees of success, and certain disadvantages are associated with each of these therapies. Although radiation therapy has shown promise, particularly in inhibiting intimal hyperplasia, the devices available for delivery of radiation sources to a stenotic site have been limited and have tended to suffer from drawbacks which limit their usefulness. Typical of the devices using radiation to treat restenosis are those shown or described in U.S. Pat. No. 5,059,166 to Fischell; U.S. Pat. No. 5,213,561 to Weinstein; U.S. Pat. No. 5,302,168 to Hess, U.S. Pat. No. 5,199,939 to Dake; U.S. Pat. No. 5,084,002 to Liprie; and U.S. Pat. No. 3,324,847 to Zoumboulis.
The present invention is directed to apparatus and methods for delivering one or more treating elements, such as a radiation source, through a catheter to a desired location in the vascular system of a human patient and to retrieving the treating element(s) through the catheter, if so desired. The present invention is particularly applicable, but not limited, to the treatment of coronary arteries that have been or will be subjected to PTCA or other artery-opening procedures, in order to inhibit intimal hyperplasia and reduce the risk of restenosis. The present invention is also useful in other areas of the vascular system, such as in the carotid artery or in coronary bypasses.
More specifically, as set forth in the appended claims, the present invention comprises an elongated flexible catheter tube having a proximal end portion adapted to remain outside the patient""s body, a distal end portion adapted to be positioned at a selected location within the vascular system of the patient and a lumen extending therebetween, with the diameter of the catheter tube being sufficiently small for insertion into the patient""s vascular system. The catheter tube is preferably but not necessarily adapted for positioning the distal end of the tube at the desired site by advancement over a guide wire. A port is provided at the proximal end portion of the tube, through which blood-compatible liquid may be introduced from a source of such liquid into the lumen. One or more treating elements, which may be in the form of a solid capsule, pellet or the like, such as a capsule or pellet containing radioactive material, is positionable within the lumen and is movable between the proximal and the distal end portions of the tube under the motive force exerted by the liquid flowing through the lumen.
In accordance with the present invention, a method is also provided for treating a selected area in the vascular system of a patient wherein an elongated flexible catheter tube having a distal end portion adapted to be positioned at a selected location within the vascular system of the patient, a proximal end portion adapted to remain outside the patient""s body, a lumen extending therebetween, and a diameter sufficiently small for insertion into the patient""s vascular system is introduced into the vascular system of a patient. The catheter is preferably but not necessarily introduced over a guide wire until the distal end portion of the tube is within the selected area of the vascular system. A port communicating with the first lumen is adapted for introduction of blood-compatible liquid into the lumen. One or more treating elements, such as a capsule or pellet containing radioactive material, is introduced into the lumen at the proximal end portion of the tube and is moved from the tube""s proximal end portion through the lumen to the distal end portion within the selected area by flowing the blood-compatible liquid through the lumen to generate a motive force on the element so as to move it from the proximal end to the desired location at the distal end portion. There, the treating element is allowed to remain a sufficient time for treatment of the selected area, during which time the remaining portion of the catheter is free of treating elements so as to not unnecessarily expose other tissue to such treatment. After the treatment is completed, the catheter tube is removed from the patient.
In another embodiment, the present invention is embodied in an angioplasty balloon catheter having proximal and distal end portions, with a lumen extending therebetween. The lumen communicates with an inflatable balloon located on the distal end portion. In accordance with the present invention, one or more treating elements, such as a radiation source, is either carried fixedly at the balloon or moved through a lumen from the proximal end portion to the distal end portion, for delivery of radiation to the stenotic site as the angioplasty procedure is actually carried outxe2x80x94therefore allowing what may otherwise be a two-step process to be carried out in a single step. From this summary, it should be apparent that the method of the present invention may be carried out before, during or after an angioplasty or other artery-opening procedure, whichever is deemed most desirable by the treating physician.